Locking arrangements for preventing screws from accidental loosening in a housing area are known. Thus, for instance, German patent DE 296 21 267 describes a device having a screw-type terminal whose screw head is covered, except for a screwdriver opening, by a covering housing, whereby this covering housing has ribs that are at a minute distance from each other, said distance being smaller than the diameter of the screw head. In this version of the state of the art, the projections of the ribs are removed by scraping as the screw head turns, so that these ribs are pushed aside by deformation. Thanks to the plastic materials, the ribs recover, so that the countersunk screw is locked in the housing area.
A type of anti-loosening lock for screws is described in G 93 08 096.4. This version—which is intended for shank screws that have a thread-free bolt section or a tapered area between the screw head and the bold thread, and that can be screwed into holes created in connecting parts—provides that the connecting part of the housing on the screw side has an integral ring of material that is pressed into the thread-free area or into the tapered area when the screw is inserted, so that the screw is locked against accidental loosening from the connecting part.
In another version, which is described in German patent DE 30 28 958, the arrangement relates to a screw lock for electric terminals, whereby the screw can be arranged so as to be countersunk into a shaft of a member or housing-like element. In this context, the vertical shaft has profiling that can be elastically deformed when the screw is inserted and when the head passes over it. After the profiling has been passed, it recovers to such an extent that it recovers over the screw head, thus completing the locking of the countersunk screw.
In these arrangements for locking the screws of electric terminals, it is considered to be a drawback that the screw locking elements that are supposed to prevent loss of the screw require very close coordination of the dimensions as well as adherence to very narrow manufacturing tolerances. The constrictions in the plastic housing are pushed aside or deformed during the insertion in such a way that loss of a screw cannot be ruled out.